Processes and systems provided herein generally relate to the field of material deposition. In particular, disclosed processes and systems provide for effective nucleation of thin films useful in various deposition techniques that grow material on a substrate to access formation of smooth and uniform thin films which may be used in microelectronics, MEMS, and other technologies.
Chemical vapor deposition (CVD) is a common technique for depositing thin films for various applications including integrated circuits, MEMS, and hard coatings. Atomic layer deposition (ALD) is another such technique, which has the capability to deposit highly conformal and uniform coatings of controlled thickness. Both of these processes begin with a nucleation step, which involves the formation of clusters of atoms of the material to be deposited onto the substrate surface. Very frequently, poor nucleation is a problem associated with these two deposition techniques. The ease of nucleation determines the film smoothness, microstructure and other properties in the later stages of film growth. For example, if nucleation is sparse, islands form on the surface and film continuity is not achieved until the layer is relatively thick. To synthesize continuous films of low thickness, the nucleation should be dense so as to avoid the existence of substrate surface with no nuclei present. On the other hand, it is important the treatment not modify the surface by sputtering, chemical reaction, etching or the like.
Reactive plasma exposure like O2, N2, NH3, H2 or halogen (F, Cl, B, I)-based gas have been used to pretreat a substrate surface prior to CVD or ALD (see U.S. Pat. Nos. 6,605,549, 6,638,859, 6,613,695). Those treatments, however, rely on reactive gases or radicals of these gases generated from the plasma, and thereby have attendant reconfiguration of surfaces. In either case, the idea is to change the surface termination from the initial state to either —OH, N, NH2 or —X terminated state, X being a halogen. This termination makes the surface more reactive to CVD/ALD precursors. Once the surface termination has changed, the CVD or ALD precursor adsorbs and reacts better on these terminations thus rendering better nucleation characteristics. That process, however, suffers from a limitation related to an interface between the film and the surface that is no longer pristine. Instead, the surface contains an additional layer of foreign atoms, which might be disadvantageous with regard to an electrical, optical and/or magnetic property of a system in which the processed surface is incorporated.
Another reported method for providing surface activation is by high-energy ion bombardment of the substrate to create defects on its surface. For example, Lim et al. (Thin Solid Films Vol. 475, p. 194) use Ar plasma exposure pretreatment to enhance nucleation of Ruthenium on a TaSiN surface. That idea, however, is based on bombarding the surface with high energy Ar+ ions, thereby etching it. Some researchers have also tried biasing the substrate to produce higher energy ion bombardment to enhance nucleation on the substrates. Such energetic pretreatment methods are not desirable in most thin film applications as they cause unwanted chemical or physical interactions with the surface, thereby interfering with functionality or adversely impacting layer geometry.
U.S. Pat. No. 6,613,695 relates to surface preparation prior to depositing a layer on the surface in an attempt to more readily nucleate poly-silicon and poly-SiGe or to more readily adsorbs ALD reactants. That process, however, pretreats by introducing relatively high energy F, Cl, H or N radicals produced by plasma product treatment. Accordingly, the surface treatment causes a change in the surface termination of the substrate to facilitate subsequent deposition. Such a change in surface termini can adversely impact desired functions and characteristics of the end system in which the processed substrate is incorporated.
Layer uniformity can become particularly problematic in conventional processing techniques used to make ultrathin layers (e.g., ultrathin gate oxides) in the less than 10 nm range. Films of such thicknesses are commonly associated with unacceptably high levels of defects, such as pinholes. The defects result in leakage currents during use, rapid device breakdown and other functional defects. Accordingly, relatively simple systems and processes capable of accessing relatively uniform and thin structures, such as thin films supported by a substrate, are needed.